这是个变的值，，建设从JTestField中输入“((3*4)+(8/4))*2+3”

然后就可以计算出值来，，

具体怎么做，？

{
程序:四则运算计算器
作者:tomm
For more Information ,please visit http://www.tommstudio.com

}


unit jsq;

interface

uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  StdCtrls, Buttons,ExtCtrls,urlmon;


const MaxElements=100;     //maximum char in stack;


type TStack=class
     private
       SData:array[1..MaxElements] of string;    //stack data
     public
       IsEmpty:boolean;                          //it is an empty stack 
       TopPointer:integer;                       //the top pointer of the stack;
       procedure Init;
       function GetElement(var data:string;i:integer):boolean;  //get data from stack
       function PopElement(var data:string):boolean;            //popup data
       function PushElement(data:string):boolean;               //push data
end;

type
  TForm1 = class(TForm)
    SpeedButton1: TSpeedButton;
    SpeedButton2: TSpeedButton;
    SpeedButton3: TSpeedButton;
    SpeedButton4: TSpeedButton;
    SpeedButton5: TSpeedButton;
    SpeedButton6: TSpeedButton;
    SpeedButton7: TSpeedButton;
    SpeedButton8: TSpeedButton;
    SpeedButton9: TSpeedButton;
    SpeedButton10: TSpeedButton;
    SpeedButton11: TSpeedButton;
    SpeedButton12: TSpeedButton;
    SpeedButton13: TSpeedButton;
    SpeedButton14: TSpeedButton;
    SpeedButton15: TSpeedButton;
    SpeedButton16: TSpeedButton;
    SpeedButton17: TSpeedButton;
    SpeedButton20: TSpeedButton;
    Panel1: TPanel;
    SpeedButton18: TSpeedButton;
    SpeedButton19: TSpeedButton;
    SpeedButton21: TSpeedButton;
    SpeedButton22: TSpeedButton;
    procedure SpeedButton1Click(Sender: TObject);
    procedure FormCreate(Sender: TObject);
    procedure SpeedButton17Click(Sender: TObject);
    procedure SpeedButton20Click(Sender: TObject);
    procedure SpeedButton19Click(Sender: TObject);
    procedure FormKeyPress(Sender: TObject; var Key: Char);
    procedure Panel1MouseMove(Sender: TObject; Shift: TShiftState; X,
      Y: Integer);
    procedure SpeedButton22Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;


  procedure StoreExpression(exp:string;mystack:TStack);          //save expression
  procedure TransformExpression(sourceStack,targetStack:TStack); //transform
  function Calculate(rStack:TStack;var Aresult:real):boolean;    //calculate

var
  Form1: TForm1;
  ExpressionStack,tempStack,ReverseStack:TStack;


implementation

{$R *.DFM}

procedure TForm1.SpeedButton1Click(Sender: TObject);
begin
  if panel1.Caption='Syntax Error' then SpeedButton17.Click;
  if TSpeedbutton(sender).caption='+/-' then begin      //+/-的处理
     if panel1.caption='0' then exit;
     if panel1.Caption[1]='-' then panel1.caption:=copy(panel1.caption,2,length(panel1.caption)) else panel1.Caption:='-'+panel1.Caption;
     exit;
  end;

  if (TSpeedbutton(Sender).caption[1] in ['0'..'9','(']) and (panel1.Caption='0') then panel1.Caption:='';       //输入数字的处理
  panel1.Caption:=panel1.Caption+TSpeedButton(Sender).caption;
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  ExpressionStack:=TStack.Create;
  tempStack:=TStack.Create;
  ReverseStack:=TStack.Create;
  ExpressionStack.Init;
  tempStack.Init;
  ReverseStack.Init;

end;


function TStack.GetElement(var data:string;i:integer):boolean;
begin
  if (i>TopPointer) or (i